Construction Design-Solar Photovoltaic

I’ve been conducting energy audits and assessments for the past 10 years, over that time, I have had several people ask me about adding a solar system to their home.  Does it make sense installing a system in Minnesota?  How about in any northern climate state?  This blog will discuss the basics of photovoltaic solar.

20 kW solar system in my community.

There are two types of photovoltaic, or electricity producing solar systems, commonly referred to as PV.  There is the grid tied system and the battery storage system.

The grid tied system is the cheaper of the two to install.  All the energy produced by the solar panels is fed into the electricity provider’s grid.  You end up with a credit on your electric bill.  One drawback is there is no power for the home to use during a power outage.  Because of the lower cost, most systems being installed today are grid tied.

A battery storage system is much more expensive to install.  The batteries are used to supplement, or in some cases, replace the electricity supplied by a power company.  There are many different ways to utilize this type of system, the batteries may just run a few different devices in the home, such as the furnace and refrigerators.  Maybe the system is just used as a back-up power source when there is a power outage.  I’ve also heard of some utility companies using this type of system for load management, some equipment within the home could be removed from the grid during peak load times, the batteries take over the power supply for that equipment.  Of course the customer receives a reduced electricity rate for allowing the control.

Nearly all PV panels produce direct current electricity.  DC is not what most homes run on, unless you live in a camper.  Alternating current (AC) is how power is supplied to homes in North America.  Because of this difference, inverters, converters and/or charge controllers are commonly needed in a battery PV system.  All this extra equipment adds cost.

All PV systems are rated at the max output of the solar panels.  Most residential systems will have an output of around 5 kilowatts, that is the max amount of electricity per hour that can be produced during full sunlight.  Of course when it’s dark, the system produces no electricity and production is reduced when it is cloudy or when the sun is lower on the horizon.

How efficient is a PV system?  One of the electricity providers in my area has installed a 20 kilowatt PV system at it’s main office.  The output of this system is tracked and posted on their website.  Over the past year, the 20 kW system has averaged 58.4 kW produced per day resulting in 12% efficiency of the systems capacity.  The average efficiency throughout the US is around 15%.  Clouds, shade and maintaining (cleaning the snow off) the panels will all effect efficiency.  Using the 5 kW system commonly installed in most homes, the listed production would be 5 kW x 24 hours per day = 120 kW.  Taking the max production and multiplying by the average efficiency in North America, this 5 kW system will produce around 18 kW per day or 540 kW per month.  If net metering (the power company purchases the electricity at the same rate it charges you for the electricity) is allowed in your area, you would end up with a credit of around $50-$60 per month.

Before installing any energy producing equipment, it is best to reduce the energy needs of your home as much as possible.  It almost always make more economic sense to reduce consumption than to add production.  Air sealing and insulating your home to make more comfortable will reduce the heating and cooling needed.  Replacing older, less efficient appliances and equipment usually will reduce the amount of electricity used by the home.  Get to know what is using electricity in your home and analyze the data to see where improvements can be made.  A tool such as a Kill A Watt meter can help track the energy use of 120 volt plug-in appliances.  Todays technology makes tracking usage much easier than even a couple years ago.

My Kill-o-watt meter

Another way to analyze electricity usage is by looking at your past electric bills.  How many kilowatts does your home use in a month.  350, 500, 1,000?  (The average usage in the state of Minnesota is 817 kW per month.) When I’m looking at past energy usage for a customer, I often look first at the months of April and May and then September and October.  Those months usually have little or no heat or air conditioning costs associated with them.  The increases in the June, July and August bill will often be air conditioning costs.  November through March increases will typically be heating related expenses.  Figuring out where reductions can be made is better than adding PV to supplement electricity costs.

Does solar make sense in Minnesota?  Minnesota ranks #13 in the country for solar installations and production.  Germany shares a similar climate to Minnesota, they produce more of their electricity from solar than the entire United States.  Yes, PV solar systems do make sense in Minnesota and other northern states.

How about costs?  According to Energysage, a 5 kW PV system in Minnesota will cost between $13,855 and $18,745 to install, this is before the 30% federal investment tax credit or any other local incentives.  The 20 year savings on an electric bill is calculated to be between $25,015 and $33,844 producing a return on investment of 7.9 to 10.7 years.   Not bad, I’d say it’s worth it.

Leave a Reply

Your email address will not be published. Required fields are marked *